The present disclosure relates generally to generators, and more particularly to slip rings used with wind turbine generators to transfer electrical current.
As energy prices have increased, wind turbines have received increased attention as environmentally safe and relatively inexpensive alternative energy sources. With this growing interest, considerable efforts have been made to develop wind turbines that are reliable and efficient.
Generally, known wind turbines include a rotor having multiple blades. The rotor is mounted to a housing or nacelle that is positioned on top of a truss or tubular tower. Utility grade wind turbines (i.e., wind turbines designed to provide electrical power to a utility grid) can have large rotors (e.g., 30 or more meters in diameter). Blades on rotors transform wind energy into a rotational torque or force that drives one or more generators that may be rotationally coupled to the rotor either directly or through a gearbox. The gearbox increases or steps up the inherently low rotational speed of the turbine rotor for the generator to efficiently convert mechanical energy to electrical energy, which is then transmitted to a utility grid.
Wind turbines including direct drive generators eliminate the gearbox, and reliability problems associated with the gearboxes. However, in at least some known direct drive or geared wind turbines, the slip rings used to transfer electrical current from a rotating shaft to a stationary member may prematurely fail. Known slip rings generally use a brush assembly to transfer the electrical current. However, such brush assemblies wear over time and generally require periodic replacement. The replacement of the brush assemblies increases the operational costs associated with the wind turbine. In some instances, replacement of the brush assemblies may require the wind turbine to be offline in a non-productive and non-operational state.
Additionally, at least some known slip ring assemblies, use mercury to transfer electrical current across the slip ring assembly. Although somewhat useful, the inclusion of mercury may adversely affect the manufacturing, distribution, operation and maintenance of the slip rings because mercury is toxic, and is a hazardous material that requires special handling.